tal requirement in exploring health and exposure associations. Full accounts of .... Insulation. Carbon cathode. Molten aluminium. Molten flux. Iron cathode bar.
Copyright ERS Journals Ltd 1994 European Respiratory Journal ISSN 0903 - 1936
Eur Respir J, 1994, 7, 165–172 DOI: 10.1183/09031936.94.07010165 Printed in UK - all rights reserved
REVIEW
Aluminium potroom asthma: the Norwegian experience J. Kongerud*+, J. Boe*, V. Søyseth**, A. Naalsund*, P. Magnus+ Aluminium potroom asthma: the Norwegian experience. J. Kongerud, J. Boe, V. Søyseth, A. Naalsund, P. Magnus. ERS Journals Ltd 1994. ABSTRACT: Work-related asthma in aluminium potroom workers, is reviewed and discussed, mainly on the basis of own investigations. The occurrence of work-related asthma has been shown to be associated with the duration of potroom employment, although the prevalence of asthmatic symptoms is not significantly different from that of the general population. Typical manifestations of occupational asthma are described in potroom workers, and a close relationship between the levels of fluoride exposure and work-related asthmatic symptoms has been observed. The existence of occupational asthma in aluminium potroom workers has been confirmed by characteristic patterns of repeated peak flow measurements, supported by changes in methacholine responsiveness in workers with suspected work-related asthma. However, no immunological test is available to establish the diagnosis. Methacholine challenge appears to be inappropriate for screening aluminium potroom workers in order to detect work-related asthma. Current smoking, but not self-reported allergy, is a risk factor for potroom asthma. A family history of asthma and previous occupational exposure may have some effect on the risk of developing symptoms. The prognosis of potroom asthma seems to depend on early replacement to unexposed work. The pathogenetic mechanisms are unknown, although some studies indirectly imply a hypersensitivity reaction. Future studies involving specific bronchial challenge appear to be necessary to find the causal agent(s) of aluminium potroom asthma. Eur Respir J., 1994, 7, 165–172.
The electrolytic production of aluminium is accompanied by emissions of dust and gases, and asthma among potroom workers in this industry has been reported for the last 60 yrs [1]. Primary aluminium production is an important industry in Norway, producing 20% of the aluminium in Europe. Asthma-like symptoms ("potroom asthma") have been the most important health problem of the workforce. Thus, the occurrence and causes of potroom asthma have been of major concern to the industry and the health authorities. This has lead to considerable scientific activity, and several papers of Norwegian origin have appeared, supporting the existence of potroom asthma [2–10]. However, in other countries there are some studies which have not been able to detect occupational asthma in the primary aluminium industry [11–14]. So far, no specific agent in the potrooms has been shown to induce a hypersensitivity reaction [15]. Therefore, controversy as to whether potroom asthma is pre-existing asthma provoked by pollutants, or asthma that is induced by agents in the work environment still remains. Disagreement with regard to the definition of occupational asthma and the use of inappropriate research methods may also explain some of the inconsistency in the published results. The purpose of the present paper was to review the published literature and to discuss the evidence that asthma can be caused by aluminium potroom exposure.
*Dept of Thoracic Medicine, Rikshospitalet, University of Oslo, Oslo, Norway. +Dept of Epidemiology, National Institute of Public Health, Oslo, Norway. **Health Department, Årdal aluminium plant, Årdalstangen, Norway. Correspondence: J. Kongerud Dept of Thoracic Medicine Rikshospitalet University of Oslo N-0027 Oslo Norway Keywords: Aluminium asthma epidemiology occupation Received: February 8 1993 Accepted after revision July 20 1993
Aluminium potroom exposure Processes used in primary aluminium production A knowledge of the potential hazards in the work atmosphere, both quantitatively and qualitatively, is a fundamental requirement in exploring health and exposure associations. Full accounts of the electrolytic processes have been published [16, 17]. Bauxite is the mineral from which aluminium is obtained. There are two stages in the process. Firstly, the separation of alumina (Al2O3) from silica, iron and other oxides, known as the Bayer process. Secondly, the transformation of alumina to aluminium by electrolysis, known as the HallHéroult process. It is the latter process which seems to be associated with development of asthma, and which will be discussed in detail. Electrolytic technology The reduction of alumina takes place in plants called smelters. The electrolytic baths or cells are usually called the pots, and the buildings where the pots are located are known as potrooms. The potrooms often extend several hundred
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metres and contain 100–200 pots. A modern single pot operates at 4–5 V and more than 150,000 A, at a temperature of about 950°C. The pots are of two types, Søderberg and prebake. The main difference between them, is the way in which the anodes are supported (figs 1 and 2). In Søderberg pots, the anode is baked on site and carbon has to be added to the top of the pot. The anodes in prebake pots are produced outside the potroom in a special department called the carbon plant. Both technologies have a steel cradle, lined with insulating material, and a cathode bottom made of carbon connected to the negative polarity of the power source. The prebake technology permits for a more automated process, with hoods covering the pot. Although
Anode beam Anode stubs
Cleaning plant ▲
Burner Anode skirt
Frozen flux and alumina Molten flux Molten aluminium Carbon cathode
the hoods are closed and the collection efficiency of the hoods for fumes is better than that seen in Søderberg, the hoods have to be removed from time to time when aluminium is tapped or when the anode has to be changed. In these situations, large amounts of pollutants are emitted. Peak levels of exposure are, therefore, more likely to occur in prebake than in Søderberg potrooms. Types of exposure The pot fume emissions are complex, and 26 substances to which exposure may occur have been listed by WALKER [18]. In a Norwegian study, personal sampling of gaseous sulphur dioxide (SO2) produced time-weighted average levels of 0.42 mg·m-3 [19], which is approximately one tenth of the Norwegian hygienic standard (8 h time-weighted average (TWA)) of 5 mg·m-3. Gaseous SO2 was also closely correlated to gaseous fluorides (r=0.67, p
